A droplet actuator is an example of digital fluidics technology. A droplet actuator typically includes one or more substrates configured to form a surface or gap for conducting droplet operations. The one or more substrates establish a droplet operations surface or gap for conducting droplet operations and may also include electrodes arranged to conduct the droplet operations via electrowetting. The droplet operations substrate or the gap between the substrates may be coated or filled with a filler fluid that is immiscible with the liquid that forms the droplets.
Optical detection systems are used with digital fluidics technology, such as with droplet actuators. The standard microscopy used in these optical detection systems remains a compromise between resolution, field of depth, and field of view. For example, using a low magnification objective (e.g., a 5× objective), the field of view is about 1 millimeter square, the field of depth is a few microns, and the resolution is a few microns. Hence, in order to capture at glance a microfluidic chamber, of which the footprint may often range from a few square millimeters to a few square centimeters and the thickness from a few microns to millimeters, standard microscopy must be motorized in order to scan both the X-Y plane and the Z focal plane. Consequently, a drawback of using standard microscopy for optical detection in, for example, a droplet actuator is the long acquisition time (a few seconds to a minute), which prevents fast time-lapse acquisition.